Multilayer thin-film structure and phase shifting device using the same

ABSTRACT

Provided are a multilayer thin-film structure and a phase shifting device using the same. The multilayer thin-film structure includes at least one crystallization preventing layer and at least one dielectric layer that are alternately stacked. The at least one crystallization preventing layer includes an amorphous material, and a thickness of the at least one crystallization preventing layer is less than a thickness of the at least one dielectric layer.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Continuation Application of U.S. application Ser. No. 16/406,677, filed May 8, 2019, which claims priority to Korean Patent Application No. 10-2018-0114373, filed on Sep. 21, 2018, in the Korean Intellectual Property Office, the disclosure of which is incorporated by reference herein in its entirety.

BACKGROUND 1. Field

Example embodiments of the present disclosure relate to a multilayer thin-film structure and a phase shifting device using the multilayer thin-film structure, and more particularly, to a multilayer thin-film structure in which a material having a high refractive index and a low extinction coefficient with respect to visible light is stacked without being crystallized and a phase shifting device operating in a visible light band using the multilayer thin-film structure.

2. Description of the Related Art

An optical device (e.g., a metamaterial) with unique electrical and optical properties that cannot be found in nature may be manufactured by using an array of dielectric structures having a size that is less than the wavelength of light. In order to manufacture such an optical device, a material having a high refractive index and a low absorption rate (i.e., a low extinction coefficient) at the wavelength of corresponding light is used. For example, silicon (Si) having a refractive index of at least 3.5 and an extinction coefficient of 1×10⁻⁵ or less is mainly used in an infrared band of a wavelength of 1550 nm. However, it is difficult to use Si in an optical device for visible light because the light absorption of Si is large at short wavelengths in the visible light band.

On the other hand, in a material having a low extinction coefficient and a high refractive index in a visible light band, a crystalline phase having a large surface roughness is more thermodynamically stable than an amorphous phase, and therefore crystallization is facilitated when the thickness of a deposited film becomes thick. As a result of the crystallization, surface roughness of the material becomes large and patterning using a conventional semiconductor process including exposure and etching processes becomes difficult.

SUMMARY

In accordance with an aspect of an example embodiment, a multilayer thin-film structure includes a crystallization preventing layer; and a dielectric layer on the crystallization preventing layer, wherein the crystallization preventing layer includes an amorphous material, a thickness of the crystallization preventing layer is less than a thickness of the dielectric layer, and the crystallization preventing layer and the dielectric layer are repeatedly stacked at least once.

The multilayer thin-film structure may further include: an amorphous substrate, wherein the dielectric layer may be on the amorphous substrate, and the crystallization preventing layer and the dielectric layer may be alternately stacked on the dielectric layer.

The multilayer thin-film structure may further include: a crystalline substrate, wherein the crystallization preventing layer and the dielectric layer may be alternately stacked on the substrate.

A refractive index of the dielectric layer in a visible light band may be 2.4 or more and an extinction coefficient of the dielectric layer may be 1×10⁻⁵ or less.

An extinction coefficient of the crystallization preventing layer in the visible light band may be 1×10⁻⁵ or less.

The dielectric layer may include an amorphous material or a crystalline material having a grain size of 100 nm or less.

The thickness of the dielectric layer may be within a range of 50 nm to 500 nm, and the thickness of the crystallization preventing layer is more than 0 nm and 10 nm or less.

A sum of thicknesses of crystallization preventing layers may be 5% or less of a total thickness of dielectric layers and crystallization preventing layers.

The crystallization preventing layer comprises amorphous silicon oxide (SiO₂), amorphous silicon nitride (Si₃N₄), or amorphous aluminum oxide (Al₂O₃).

The dielectric layer may include amorphous titanium oxide (TiO₂), amorphous gallium phosphide (GaP), amorphous gallium nitride (GaN), or amorphous aluminum arsenide (AlAs).

A root mean square (RMS) value of surface roughness of an uppermost surface of the multilayer thin-film structure is 2.5 nm or less.

In accordance with an aspect of an example embodiment, a phase shifting device includes: a plurality of phase shift patterns having a size less than the wavelength of visible light, wherein each of the phase shift patterns includes a crystallization preventing layer and a dielectric layer that are stacked repeatedly at least once, wherein the crystallization preventing layer includes an amorphous material, and a thickness of the crystallization preventing layer is less than a thickness of the dielectric layer.

Each of the phase shift patterns may have the form of a bar or a slit extending in a first direction, and the plurality of phase shift patterns may be one-dimensionally arranged in a second direction perpendicular to the first direction.

The plurality of phase shift patterns may be two-dimensionally arranged and each of the phase shift patterns may have a square, rectangular, circular, or oval shape.

The phase shifting device may be applied to a flat lens, a planar color filter, a flat beam deflector, or a planar spectroscope in a visible light band or a near-infrared band.

In accordance with an aspect of an example embodiment, a multilayer thin-film structure includes at least one crystallization preventing layer; and at least one dielectric layer, wherein the at least one crystallization preventing layer comprises an amorphous material, wherein a thickness of the at least one crystallization preventing layer is less than a thickness of the at least one dielectric layer, and wherein the at least one crystallization preventing layer and the at least one dielectric layer are alternately stacked.

The multilayer thin-film structure may further include an amorphous substrate, wherein a lowermost dielectric layer from among the at least one dielectric layer is disposed on the amorphous substrate.

The multilayer thin-film structure may further include a crystalline substrate, wherein the at least one crystallization preventing layer and the at least one dielectric layer are alternately stacked on the crystalline substrate.

A refractive index of the at least one dielectric layer in a visible light band may be greater than or equal to 2.4 and an extinction coefficient of the at least one dielectric layer in the visible light band is less than or equal to 1×10⁻⁵.

An extinction coefficient of the at least one crystallization preventing layer in the visible light band may be less than or equal to 1×10⁻⁵

The at least one dielectric layer may include a crystalline material having a grain size that is less than or equal to 100 nm or an amorphous material.

The thickness of the at least one dielectric layer may be within a range of 50 nm to 500 nm, and the thickness of the at least one crystallization preventing layer may be less than or equal to 10 nm.

A sum of thicknesses of all of the at least one crystallization preventing layer may be less than or equal to 5% a total thickness of all of the at least one dielectric layer and all of the at least one crystallization preventing layer.

The at least one crystallization preventing layer may include amorphous silicon oxide (SiO₂), amorphous silicon nitride (Si₃N₄), or amorphous aluminum oxide (Al₂O₃).

The at least one dielectric layer may include amorphous titanium oxide (TiO₂), amorphous gallium phosphide (GaP), amorphous gallium nitride (GaN), or amorphous aluminum arsenide (AlAs).

A root mean square value of surface roughness of an uppermost surface of the multilayer thin-film structure may be less than or equal to 2.5 nm.

In accordance with an aspect of an example embodiment, a phase shifting device includes a plurality of phase shift patterns, each of the plurality of phase shift patterns having at least one dimension smaller than a wavelength of visible light, wherein each of the plurality of phase shift patterns comprises at least one crystallization preventing layer and at least one dielectric layer that are alternately stacked, wherein the at least one crystallization preventing layer comprises an amorphous material, and wherein a thickness of the at least one crystallization preventing layer is less than a thickness of the at least one dielectric layer.

The phase shifting device may further include an amorphous substrate, wherein each phase shift pattern from among the plurality of phase shift patterns comprises a lowermost dielectric layer from among the at least one dielectric layer, the lowermost dielectric layer being stacked on the amorphous substrate.

The phase shifting device may further include a crystalline substrate, and each phase shift pattern from among the plurality of phase shift patterns comprises the at least one crystallization preventing layer and the at least one dielectric layer that are alternately stacked on the crystalline substrate.

A refractive index of the at least one dielectric layer in a visible light band may be greater than or equal to 2.4 and an extinction coefficient of the at least one dielectric layer in the visible light band may be less than or equal to 1×10⁻⁵.

An extinction coefficient of the at least one crystallization preventing layer in the visible light band may be less than or equal to 1×10⁻⁵.

The at least one dielectric layer may include a crystalline material having a grain size that is less than or equal to 100 nm or an amorphous material.

The thickness of the at least one dielectric layer may be within a range of 50 nm to 500 nm, and the thickness of the at least one crystallization preventing layer may be less than or equal 10 nm.

A sum of thicknesses of all of the at least one crystallization preventing layer present in each phase shift pattern from among the plurality of phase shift patterns may be less than or equal to 5% of a total thickness of all of the at least one dielectric layer and all of the at least one crystallization preventing layer present in each shift pattern from among the plurality of phase shift patterns.

The at least one crystallization preventing layer may include amorphous silicon oxide (SiO₂), amorphous silicon nitride (Si₃N₄), or amorphous aluminum oxide (Al₂O₃), and the at least one dielectric layer may include amorphous titanium oxide (TiO₂), amorphous gallium phosphide (GaP), amorphous gallium nitride (GaN), or amorphous aluminum arsenide (AlAs).

A root mean square value of surface roughness of an uppermost surface of each of the plurality of phase shift patterns may be less than or equal to 2.5 nm.

Each phase shift pattern from among the plurality of phase shift patterns may include a bar or a slit extending in a first direction, and the plurality of phase shift patterns may be arranged in a second direction perpendicular to the first direction.

The plurality of phase shift patterns may be two-dimensionally arranged and each phase shift pattern from among the plurality of phase shift patterns may have a square, rectangular, circular, or oval shape.

The phase shifting device may be applied to a flat lens, a planar color filter, a flat beam deflector, or a planar spectroscope, and the phase shifting device may be configured to shift a phase of incident light in a visible light band or a near-infrared band.

In accordance with an aspect of an example embodiment, a thin-film metamaterial includes alternately stacked dielectric amorphous layers and crystallization preventing amorphous layers, wherein a thickness of each of the dielectric amorphous layers is less than a thickness at which the dielectric amorphous layers crystallize.

A thickness of each of the crystallization preventing amorphous layers may be less than the thickness of each of the dielectric amorphous layers.

The thickness of each of the crystallization preventing amorphous layers may be less than or equal to 10 nm, and the thickness of each of the dielectric amorphous layers may be within a range of 50 nm to 500 nm.

A refractive index in a visible light band of the dielectric amorphous layers may be greater than or equal to 2.4 and an extinction coefficient in the visible light band of the dielectric amorphous layers may be less than or equal to 1×10⁻⁵.

An extinction coefficient in the visible light band of the crystallization preventing amorphous layers may be less than or equal to 1×10⁻⁵.

An uppermost layer of the thin-film metamaterial may be a dielectric amorphous layer, and a root mean square value of a surface roughness of the uppermost layer may be less than or equal to 2.5 nm.

The thin-film metamaterial may further include a plurality of structures formed on a substrate, each of the plurality of structures including the alternately stacked dielectric amorphous layers and crystallization preventing amorphous layers.

A width of each of the plurality of structures may be less than a wavelength of visible light.

An interval between each of the plurality of structures may be less than a wavelength of visible light.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and/or other aspects will become apparent and more readily appreciated from the following description of example embodiments, taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a cross-sectional view of a configuration of a multilayer thin-film structure according to an example embodiment;

FIG. 2 is a cross-sectional view of a configuration of a multilayer thin-film structure according to an example embodiment;

FIG. 3 is a cross-sectional view of an example of fabrication of the multilayer thin-film structure shown in FIG. 1;

FIG. 4 is a graph showing a change in reflectivity according to the thickness of a crystallization preventing layer in the multilayer thin-film structure shown in FIG. 3;

FIG. 5 is a cross-sectional photograph of an actually manufactured multilayer thin-film structure;

FIG. 6 is a photograph showing an upper surface of the multilayer thin-film structure shown in FIG. 5;

FIG. 7 is a photograph showing a cross-section and an upper surface of a thin-film structure according to a comparative example;

FIG. 8 is a photograph showing a cross-section and an upper surface of the thin-film structure shown in FIG. 7 after increasing the thickness of the thin-film structure;

FIG. 9 is a graph illustrating a refractive index of a multilayer thin-film structure according to an example embodiment;

FIG. 10 is a cross-sectional view of a structure of a phase shifting device according to an example embodiment;

FIG. 11 is a perspective view of a form of exemplary phase shift patterns of a phase shifting device according to an example embodiment;

FIG. 12 is a perspective view of a form of exemplary phase shift patterns of a phase shifting device according to an example embodiment;

FIG. 13 is a perspective view of a form of exemplary phase shift patterns of a phase shifting device according to an example embodiment;

FIG. 14 is a perspective view of a form of exemplary phase shift patterns of a phase shifting device according to an example embodiment;

FIG. 15 is a photograph of a surface of a phase shifting device actually manufactured so as to have a nano-lattice phase shift pattern;

FIG. 16 is a photograph of a surface of a phase shifting device actually manufactured so as to have a nano-column phase shift pattern;

FIG. 17 is a graph showing a phase shift according to a change in widths of phase shift patterns in the phase shifting devices shown in FIGS. 15 and 16;

FIG. 18 is a view of the arrangement of nano-column phase shift patterns of a flat lens according to an example embodiment;

FIG. 19 is a graph of an example of a phase shift according to the position of the flat lens shown in FIG. 18;

FIG. 20 is a cross-sectional view of an example of an operation of the flat lens shown in FIG. 18;

FIG. 21 is a view of the arrangement of nano-column phase shift patterns of a flat beam deflector according to an example embodiment;

FIG. 22 is a graph of an example of a phase shift according to a position of the flat beam deflector shown in FIG. 21; and

FIG. 23 is a cross-sectional view of an example of an operation of the flat beam deflector shown in FIG. 21.

DETAILED DESCRIPTION

Hereinafter, a multilayer thin-film structure and a phase shifting device using the same will be described in detail with reference to the accompanying drawings. The same reference numerals refer to the same elements throughout. In the drawings, the sizes of constituent elements may be exaggerated for clarity. The embodiments described below are merely examples, and various modifications may be possible. In a layer structure described below, an expression such as “above” or “on” may include not only the meaning of “immediately on/under/to the left/to the right in a contact manner”, but also the meaning of “on/under/to the left/to the right in a non-contact manner”.

FIG. 1 is a cross-sectional view of a configuration of a multilayer thin-film structure 10 according to an example embodiment. Referring to FIG. 1, the multilayer thin-film structure 10 according to an example embodiment includes a structure in which crystallization preventing layers 13 (i.e., crystallization preventing amorphous layers) and transparent dielectric layers 12 (i.e., dielectric amorphous layers) are alternately stacked. The transparent dielectric layers 12 may have a high refractive index. In the present example embodiment, the high refractive index may be defined as a refractive index of about 2.4 or more, which is higher by about 1.4 or more than the refractive index of air in a visible light band (450 nm to 750 nm) or a near infrared band (750 nm to 1000 nm). The term “transparent” may mean that an extinction coefficient is 1×10⁻⁵ or less in the visible infrared band or the near-infrared band. The material of a transparent dielectric layer 12 of high refractive index satisfying these conditions may include, for example, titanium oxide (TiO₂), gallium phosphide (GaP), gallium nitride (GaN), or aluminum arsenide (AlAs). All of these materials have an extinction coefficient of 1×10⁻⁵ or less at a wavelength of 550 nm. In addition, the refractive index of TiO₂ is about 2.453 at a wavelength of 550 nm, the refractive index of GaP is about 3.450 at a wavelength of 550 nm, the refractive index of GaN is about 2.408 at a wavelength of 550 nm, and the refractive index of AlAs is about 3.248 at a wavelength of 550 nm.

As a thickness of materials such as TiO₂, GaP, GaN, AlAs, and the like increases, a root means square (RMS) value of a surface roughness also increases due to crystallization. Therefore, it is difficult to manufacture a nanostructure having a critical dimension of 100 nm or less. Crystallization of the dielectric layer 12 may be suppressed by inserting crystallization preventing layer 13 between the dielectric layers 12. The crystallization preventing layer 13 may include a material having an extinction coefficient of 1×10⁻⁵ or less in a visible light band or a near-infrared band while stably maintaining an amorphous state instead of a crystalline state. For example, the material of the crystallization preventing layer 13 satisfying these conditions may include amorphous silicon oxide (SiO₂), amorphous silicon nitride (Si₃N₄), or amorphous aluminum oxide (Al₂O₃).

Alternatively, the crystallization preventing layer 13 may be formed by performing ion implantation on a surface of the dielectric layer 12. For example, after the dielectric layer 12 is formed, a noble element such as argon (Ar), krypton (Kr), xenon (Xe), neon (Ne), or the like, a Group IV element such as silicon (Si), germanium (Ge), or the like, a Group III element such as boron (B), gallium (Ga), indium (In), or the like, or a Group V element such as nitrogen(N), phosphorus (P), arsenide (As), antimony (Sb), or the like is ion-implanted into the surface of the dielectric layer 12. Then, the above-mentioned ions are intensively distributed on the surface of the dielectric layer 12 to form the crystallization preventing layer 13. Next, another dielectric layer 12 may be deposited again onto the ion-implanted surface of the previous dielectric layer 12.

The multilayer thin-film structure 10 may also include an amorphous substrate 11. For example, the substrate 11 may include glass, quartz, fused silica, or amorphous Al₂O₃.

When the substrate 11 includes an amorphous material, the dielectric layer 12 may be deposited first on the substrate 11. The crystallization preventing layer 13 may be deposited on the dielectric layer 12, and the dielectric layer 12 may be deposited again on the crystallization preventing layer 13. In this manner, the dielectric layers 12 and the crystallization preventing layers 13 may be alternately stacked. The deposition method of the dielectric layer 12 and the crystallization preventing layer 13 may include, for example, sputtering, E-beam evaporation, plasma-enhanced chemical vapor deposition (PECVD) metalorganic vapor phase epitaxy sputtering (MOCVD), atomic layer deposition (ALD), and the like. Alternatively, the crystallization preventing layer 13 may be formed by implanting ions into the surface of the dielectric layer 12 by ion implantation after the dielectric layer 12 is deposited by the above-described vapor deposition methods.

Although FIG. 1 illustratively shows that four dielectric layers 12 and three crystallization preventing layers 13 are stacked on the substrate 11, this is only an example. For example, the multilayer thin-film structure 10 may include only two dielectric layers 12 and only one crystallization preventing layer 13, or may include only three dielectric layers 12 and only two crystallization preventing layers 13. In addition, a larger number of dielectric layers 12 and crystallization preventing layers 13 than those shown in FIG. 1 may be stacked. For example, a total thickness of the dielectric layers 12 and the crystallization preventing layers 13 may be within a range of about 200 nm to about 2000 nm, and the number of dielectric layers 12 and the number of crystallization preventing layers 13 may be determined considering the thickness of each dielectric layer 12 and the thickness of each crystallization preventing layer 13.

The dielectric layers 12 may be crystallized during the stacking process if the thickness of the dielectric layers 12 is too large. Therefore, the dielectric layer 12 may be stacked only to the extent that the dielectric layer 12 is not crystallized, and then the crystallization preventing layer 13 may be stacked thereon. For example, the thickness of one dielectric layer 12 may be within a range of about 50 nm to about 500 nm. The thickness of one dielectric layer 12 may be less than a thickness at which the dielectric layer is crystallized.

FIG. 2 is a cross-sectional view of a configuration of a multilayer thin-film structure 10 a according to another example embodiment. Referring to FIG. 2, the multilayer thin-film structure 10 a may include a substrate 11 formed of a crystalline material. In this case, when the dielectric layer 12 is directly stacked on the substrate 11, the dielectric layer 12 itself may also be crystallized. Therefore, the determination of whether to stack the crystallization preventing layer 13 or the dielectric layer 12 directly on the substrate 11 may depend on the type of the substrate 11. When the substrate 11 is crystalline, as shown in FIG. 2, the crystallization preventing layer 13 is first deposited on the substrate 11, and the dielectric layer 12 is deposited thereon.

Regardless of the type of the substrate 11, the dielectric layer 12 is always located at the top of the multilayer thin-film structure 10 shown in FIG. 1 and the multilayer thin-film structure 10 a shown in FIG. 2. Therefore, when the substrate 11 is amorphous, the number of dielectric layers 12 is one more than the number of crystallization-preventing layers 13. When the substrate 11 is crystalline, the number of dielectric layers 12 is identical to the number of crystallization preventing layers 13.

Since a refractive index of the crystallization preventing layer 13 is less than that of the dielectric layer 12, the multilayer thin-film structures 10 and 10 a may lose high refractive index characteristics when the ratio of the crystallization preventing layer 13 in the multilayer thin-film structures 10 and 10 a is increased. The multilayer thin-film structure 10 is simulated in order to examine an influence of the dielectric layer 12. For example, FIG. 3 is a cross-sectional view of an example of fabrication of the multilayer thin-film structure 10 shown in FIG. 1. Referring to FIG. 3, three dielectric layers 12 and two crystallization preventing layers 13 are alternately stacked on a glass substrate 11. Here, it is assumed that the dielectric layer 12 has a thickness of 200 nm and includes TiO₂, and the crystallization preventing layer 13 includes SiO₂.

FIG. 4 is a graph showing a change in reflectivity according to a thickness of the crystallization preventing layer 13 in the multilayer thin-film structure shown in FIG. 3. Referring to FIG. 4, when there is no crystallization preventing layer 13, that is, when the thickness of the crystallization preventing layer 13 is 0 nm, the reflectivity of the multilayer thin-film structure 10 is about 4%. When the thickness of the crystallization preventing layer 13 is 5 nm, the reflectivity of the multilayer thin-film structure 10 is maintained at about 4%. However, as the thickness of the crystallization preventing layer 13 further increases, the reflectivity of the multilayer thin-film structure 10 gradually increases. In particular, it can be seen that the reflectivity of the multilayer thin-film structure 10 greatly increases from about 8% to 38% as the thickness of the crystallization preventing layer 13 increases from 10 nm to 20 nm. As a result, when the ratio of the crystallization preventing layer 13 in the multilayer thin-film structures 10 and 10 a is increased, not only do the multilayer thin-film structures 10 and 10 a lose high refractive index characteristics, but also the light transmittance of the multilayer thin-film structures 10 and 10 a is lowered.

In consideration of these results, the thickness of the crystallization preventing layer 13 may be much less than the thickness of one dielectric layer 12. For example, the thickness of the crystallization preventing layer 13 may be more than 0 nm and not more than about 10 nm. In addition, a sum of thicknesses of all the crystallization preventing layers 13 in the structure may be limited to 5% or less of a total thickness of all the dielectric layers 12 and all the crystallization preventing layers 13 in the structure.

FIG. 5 is a cross-sectional photograph of an actually manufactured multilayer thin-film structure 10. Referring to FIG. 5, TiO₂ is deposited as the dielectric layer 12 on the glass substrate 11 to a thickness of about 200 nm, SiO₂ is deposited as the crystallization preventing layer 13 to a thickness of about 5 nm, and another layer of TiO₂ is deposited thereon as the dielectric layer 12 to a thickness of about 200 nm.

Furthermore, FIG. 6 is a photograph showing an upper surface of the multilayer thin-film structure 10 shown in FIG. 5. The photograph shown in FIG. 6 shows an uppermost surface of the multilayer thin-film structure 10 obliquely taken at an angle of about 50° with respect to the surface normal. Referring to FIG. 6, it can be seen that the uppermost surface of the multilayer thin-film structure 10 is very smooth.

FIG. 7 is a photograph, which is obliquely taken at an angle of about 50°, showing both a cross-section and an upper surface of a thin-film structure according to a comparative example. In the photograph shown in FIG. 7, TiO₂ is deposited on a glass substrate to a thickness of about 210 nm to form the thin-film structure according to the comparative example. Referring to FIG. 7, it can be seen that TiO₂ is not crystallized up to a thickness of 210 nm, and an upper surface of the thin-film structure is smooth.

FIG. 8 is a photograph, which is obliquely taken at an angle of about 50°, showing both a cross-section and an upper surface of the thin-film structure shown in FIG. 7 after increasing the thickness of the thin-film structure. Referring to FIG. 8, when TiO₂ is continuously deposited and the thickness becomes about 415 nm, coarse crystal grains are seen on an upper surface of TiO₂ because TiO₂ is partially crystallized as a result of the increased thickness of the TiO₂.

As described above, crystallization of materials of the dielectric layer 12 may be prevented while maintaining the thickness of the multilayer thin-film structures 10 and 10 a by inserting the crystallization preventing layer 13 between dielectric layers 12. Therefore, the material of the dielectric layer 12 in the multilayer thin-film structures 10 and 10 a according to the present example embodiment may maintain an amorphous state. Alternatively, the material of the dielectric layer 12 may be partially crystallized, but the size of crystal grains may be suppressed to 100 nm or less. Then, RMS values of surface roughnesses of uppermost surfaces of the multilayer thin-film structures 10 and 10 a may be maintained at 2.5 nm or less.

FIG. 9 is a graph illustrating a refractive index of the multilayer thin-film structure 10 according to an example embodiment. The multilayer thin-film structure 10 has a structure in which 5 nm thick SiO₂ is inserted between TiO₂ having a total thickness of 400 nm. FIG. 9 shows refractive indices of Si₃N₄, Al₂O₃, SiO₂, and TiO₂, none of which includes the crystallization preventing layer 13, together for comparison. Referring to the graph of FIG. 9, it can be seen that the refractive index of the multilayer thin-film structure 10 is much greater than the refractive indices of Si₃N₄, Al₂O₃, and SiO₂ and is substantially similar to the refractive index of TiO₂ that does not include the crystallization preventing layer 13. For example, the refractive index of the multilayer thin-film structure 10 at a wavelength of 550 nm is only 0.013 less than the refractive index of TiO₂. Therefore, even when the crystallization preventing layer 13 is interposed between the dielectric layers 12, it can be seen that when the thickness of the crystallization preventing layer 13 is small, high refractive index characteristics are maintained.

As described above, the multilayer thin-film structures 10 and 10 a may have a sufficiently high refractive index and a sufficiently low extinction coefficient in a visible light band or a near-infrared band. Further, since the dielectric layer 12 is entirely or almost entirely amorphous, the surface roughness of an upper surface of the multilayer thin-film structures 10 and 10 a may be sufficiently low. Thus, the multilayer thin-film structures 10 and 10 a may be patterned into a nanoscale pattern using a conventional semiconductor process including exposure and etching. By patterning the multilayer thin-film structures 10 and 10 a into the nanoscale pattern, it is possible to manufacture various optical devices operating in the visible light band or the near-infrared band.

For example, FIG. 10 is a cross-sectional view of a structure of a phase shifting device 20 according to an example embodiment. Referring to FIG. 10, the phase shifting device 20 may include a plurality of phase shift patterns 15 (i.e., structures) having at least one dimension smaller than the wavelength of visible light. Here, the plurality of phase shift patterns 15 may be formed by patterning the multilayer thin-film structures 10 and 10 a. Therefore, each of the phase shift patterns 15 may include the crystallization preventing layers 13 and the transparent dielectric layers 12 of high refractive index, which are stacked repeatedly at least once.

As described above, when the substrate 11 is an amorphous substrate, each phase shift pattern 15 includes a multilayer thin-film structure in which the dielectric layers 12 and the crystallization preventing layers 13 are repeatedly stacked in this order on the substrate 11 and the dielectric layer 12 is arranged on the top surface. When the substrate 11 is a crystalline substrate, each phase shift pattern 15 includes a multilayer thin-film structure in which the crystallization preventing layers 13 and the dielectric layers 12 are repeatedly stacked on the substrate 11 in this order. In addition, the structure of the phase shift patterns 15 may be the same as the structure of the multilayer thin-film structures 10 and 10 a including the dielectric layers 12 and the crystallization preventing layers 13.

A width W of each phase shift pattern 15, an interval S between each two adjacent phase shift patterns 15, and a height H of each phase shift pattern 15 may be variously determined depending on an application of the phase shifting device 20 and the wavelength of incident light. Either or both of the width W of each phase shift pattern 15 and the interval S between two adjacent phase shift patterns 15 may be less than the wavelength of visible light so as to operate in the visible light band or the near-infrared band. For example, the width W of each phase shift pattern 15 and the spacing S between two adjacent phase shift patterns 15 may be within a range of 100 nm to 700 nm. In addition, the height H of each phase shift pattern 15 may be within a range of 200 nm to about 2000 nm.

Depending on the desired optical characteristics of a phase shifting device 20 to be formed, the plurality of phase shift patterns 15 may have various shapes and arrangements. The width W of each phase shift pattern 15 or the interval S between two adjacent phase shift patterns 15 may vary locally depending on the position on the phase shifting device 20. For example, the width W of each phase shift pattern 15 or the interval S between two adjacent phase shift patterns 15 may gradually increase or decrease, or may vary irregularly. The plurality of phase shift patterns 15 may be arranged non-periodically within the entire area of the phase shifting device 20 or locally periodically within a specific area on the phase shifting device 20.

For example, FIG. 11 is a perspective view of a form of exemplary phase shift patterns 15 of a phase shifting device 20 a according to an example embodiment. Referring to FIG. 11, each of the phase shift patterns 15 may have the form of a bar extending in a first direction. The plurality of phase shift patterns 15 may be arranged in a second direction perpendicular to the first direction. The plurality of phase shift patterns 15 may have different widths W. FIG. 11 shows that the widths W of the phase shift patterns 15 are gradually reduced in the second direction, but this is only an example. Depending on other designs, the widths W of the phase shift patterns 15 may change periodically or irregularly. Also, the plurality of phase shift patterns 15 may have an identical width W, and the interval S between the phase shift patterns 15 may instead be different.

FIG. 12 is a perspective view of a form of exemplary phase shift patterns 15 of a phase shifting device 20 b according to another example embodiment. Referring to FIG. 12, in contrast to the bar form shown in FIG. 11, each of the phase shift patterns 15 may have the form of a slit extending in a first direction. The plurality of phase shift patterns 15 may be arranged in a second direction perpendicular to the first direction. For example, the phase shifting device 20 a shown in FIG. 12 may be manufactured by forming a straight groove in the multilayer thin-film structures 10 and 10 a via a general semiconductor process.

Furthermore, FIG. 13 is a perspective view of a form of exemplary phase shift patterns 15 of a phase shifting device 20 c according to another example embodiment. Referring to FIG. 13, each of the phase shift patterns 15 may have a square or rectangular shape. Then, the plurality of phase shift patterns 15 may be two-dimensionally arranged. Either or both of the width W of the plurality of phase shift patterns 15 or the interval S between the plurality of phase shift patterns 15 may vary locally depending on a position on the phase shifting device 20 c. The phase shifting device 20 c may be manufactured by patterning the multilayer thin-film structures 10 and 10 a via a general semiconductor process.

Furthermore, FIG. 14 is a perspective view of a form of exemplary phase shift patterns 15 of a phase shifting device 20 d according to another example embodiment. Referring to FIG. 14, each of the phase shift patterns 15 may have a circular or oval shape, and the plurality of phase shift patterns 15 may be two-dimensionally arranged.

In addition, each of the phase shift patterns 15 may have various shapes. For example, each of the phase shift patterns 15 may have another polygonal shape, such as a hexagon. In addition, each of the phase shift patterns 15 may be a hole having a circular, oval, or polygonal shape.

FIG. 15 is a photograph of a surface of a phase shifting device actually manufactured so as to have a nano-lattice phase shift pattern 15. The phase shift pattern 15 is formed by forming the multilayer thin-film structure 10 to a height of 400 nm using TiO₂ and SiO₂ and then patterning the multilayer thin-film structure 10 through exposure and etching processes.

FIG. 16 is a photograph of a surface of a phase shifting device actually manufactured so as to have nano-column phase shift patterns 15. Each phase shift pattern 15 has a cylindrical shape. The phase shift pattern 15 is formed by forming the multilayer thin-film structure 10 to a height of 200 nm using TiO₂ and SiO₂ and then patterning the multilayer thin-film structure 10 through exposure and etching processes.

FIG. 17 is a graph showing a phase shift according to a change in widths or diameters of the phase shift patterns 15 in the phase shifting devices shown in FIGS. 15 and 16. In FIG. 17, G1, G2, G3, and G4 denote phase shifting devices having nano-lattice phase shift patterns 15 having different widths, and P1, P2, P3, and P4 denote phase shifting devices having nano-column phase shift patterns 15 having different diameters.

Referring to FIG. 17, phase delays for each of widths of the phase shift patterns 15 of 120 nm, 180 nm, 240 nm, and 300 nm in the phase shifting devices having the nano-lattice phase shift patterns 15 are 126°, 81°, 31°, and −8°, respectively. Therefore, as the widths of the phase shift patterns 15 increase, the phase delays decrease. A difference between the maximum phase delay and the minimum phase delay in the phase shifting devices with the illustrated nano-lattice phase shift patterns 15 is 134°.

Furthermore, for the phase shifting devices having the nano-column phase shift patterns 15, phase delays for each of diameters of the phase shift patterns 15 of 120 nm, 180 nm, 240 nm, and 300 nm in the phase shifting devices are 167°, 147°, 101°, and 93°, respectively. Therefore, as the diameters of the phase shift patterns 15 increase, the phase delays decrease. A difference between the maximum phase delay and the minimum phase delay in the phase shifting devices with the illustrated nano-column phase shift patterns 15 is 74°.

With such phase shifting devices, it is possible to condense incident light, scatter or reflect incident light in a specific direction, change a traveling direction of incident light, or transmit or reflect only light of a specific wavelength among incident light. In particular, it is possible to manufacture an optical device that exceeds a physical limitation of a diffraction phenomenon in a visible light band or a near-infrared wavelength band by implementing a line width of ¼ or less of the wavelength of the light by using a material having a high refractive index and a low extinction coefficient in the visible light band or the near-infrared wavelength band. Operating characteristics of the optical device may be determined according to phase shift distribution by arrangement of the phase shift patterns 15.

For example, FIG. 18 is a view of the arrangement of the nano-column phase shift patterns 15 of a flat lens 30 according to an example embodiment. Referring to FIG. 18, a plurality of phase shift patterns 15 having a cylindrical shape are arranged on the substrate 11 in the form of concentric circles. Diameters of the phase shift patterns 15 vary depending on position on the flat lens 30 and the phase shift patterns 15 arranged at an identical radial position from the center of the flat lens 30 may have an identical diameter. In other words, each concentric circle of phase shift patterns 15 have may a uniform diameter.

FIG. 19 is a graph of an example of a resultant phase shift according to a position of the flat lens 30 shown in FIG. 18. In FIG. 19, the horizontal axis denotes a position in a cross-section across the center of the flat lens 30, and the vertical axis denotes phase delay. Diameters of the phase shift patterns 15 may vary in a radial direction from the center of the flat lens 30 so as to have the phase delay shown in FIG. 19.

FIG. 20 is a cross-sectional view of an example of an operation of the flat lens 30 shown in FIG. 18. As shown in FIG. 20, the flat lens 30 having the phase delay distribution as shown in FIG. 19 may serve as a lens for condensing incident light. The flat lens 30 may be manufactured to a very small thickness of 1 μm or less, and thus may be employed in a small optical device or a small electronic device.

FIG. 21 schematically shows the arrangement of the nano-column phase shift patterns 15 of a flat beam deflector 40 according to an example embodiment. Referring to FIG. 21, the plurality of phase shift patterns 15 having a straight bar shape are arranged on the substrate 11. Widths of the phase shift patterns 15 decrease and intervals between the phase shift patterns 15 increase toward the right side.

FIG. 22 is a graph of an example of a resultant phase shift according to a position of the flat beam deflector 40 shown in FIG. 21. Referring to FIG. 22, phase delays increase toward the right side of the flat beam deflector 40.

FIG. 23 is a cross-sectional view of an example of an operation of the flat beam deflector 40 shown in FIG. 21. As shown in FIG. 23, the flat beam deflector 40 having the phase delay distribution as shown in FIG. 22 may change the traveling direction of incident light to a specific direction.

Various applications are possible in addition to the flat lens 30 and the flat beam deflector 40 shown in FIGS. 18 to 23. For example, a phase shifting device may be applied to a planar color filter, a planar spectroscope, or the like, which operates in a visible light band or a near-infrared band. In addition, the phase shifting device may be formed in an on-chip form on a semiconductor circuit structure such as an image sensor, a display device, a spatial light modulator, and the like.

Although the multilayer thin-film structure and the phase shifting device using the same have been described above with reference to the embodiments shown in the drawings, they are only examples. It should be understood that example embodiments described herein should be considered in a descriptive sense only and not for purposes of limitation. The scope of rights is indicated in the claims rather than the above description, and all differences within the scope of equivalents should be construed as being included in the scope of rights. 

What is claimed is:
 1. A multilayer thin-film structure comprising: at least one crystallization preventing layer; and at least one dielectric layer, wherein the at least one crystallization preventing layer comprises an amorphous material, wherein a thickness of the at least one crystallization preventing layer is less than a thickness of the at least one dielectric layer, and wherein the at least one crystallization preventing layer and the at least one dielectric layer are alternately stacked, wherein a root mean square value of surface roughness of an uppermost surface of the multilayer thin-film structure is less than or equal to 2.5 nm.
 2. The multilayer thin-film structure of claim 1, further comprising: an amorphous substrate, wherein a lowermost dielectric layer from among the at least one dielectric layer is disposed on the amorphous substrate.
 3. The multilayer thin-film structure of claim 1, further comprising: a crystalline substrate, wherein the at least one crystallization preventing layer and the at least one dielectric layer are alternately stacked on the crystalline substrate.
 4. The multilayer thin-film structure of claim 1, wherein a refractive index of the at least one dielectric layer in a visible light band is greater than or equal to 2.4 and an extinction coefficient of the at least one dielectric layer in the visible light band is less than or equal to 1×10−5.
 5. The multilayer thin-film structure of claim 4, wherein an extinction coefficient of the at least one crystallization preventing layer in the visible light band is less than or equal to 1×10−5.
 6. The multilayer thin-film structure of claim 1, wherein the at least one dielectric layer comprises a crystalline material having a grain size that is less than or equal to 100 nm or an amorphous material.
 7. The multilayer thin-film structure of claim 1, wherein the thickness of the at least one dielectric layer is within a range of 50 nm to 500 nm, and the thickness of the at least one crystallization preventing layer is less than or equal to 10 nm.
 8. The multilayer thin-film structure of claim 7, wherein a sum of thicknesses of all of the at least one crystallization preventing layer is less than or equal to 5% a total thickness of all of the at least one dielectric layer and all of the at least one crystallization preventing layer.
 9. A phase shifting device comprising: a plurality of phase shift patterns, each of the plurality of phase shift patterns having at least one dimension smaller than a wavelength of visible light, wherein each of the plurality of phase shift patterns comprises at least one crystallization preventing layer and at least one dielectric layer that are alternately stacked, wherein the at least one crystallization preventing layer comprises an amorphous material, and wherein a thickness of the at least one crystallization preventing layer is less than a thickness of the at least one dielectric layer, wherein a root mean square value of surface roughness of an uppermost surface of each of the plurality of phase shift patterns is less than or equal to 2.5 nm.
 10. The phase shifting device of claim 9, further comprising: an amorphous substrate, wherein each of the plurality of phase shift patterns comprises a lowermost dielectric layer from among the at least one dielectric layer, the lowermost dielectric layer being stacked on the amorphous substrate.
 11. The phase shifting device of claim 9, further comprising: a crystalline substrate, and each of the plurality of phase shift patterns comprises the at least one crystallization preventing layer and the at least one dielectric layer that are alternately stacked on the crystalline substrate.
 12. The phase shifting device of claim 11, wherein a refractive index of the at least one dielectric layer in a visible light band is greater than or equal to 2.4 and an extinction coefficient of the at least one dielectric layer in the visible light band is less than or equal to 1×10−5.
 13. The phase shifting device of claim 12, wherein an extinction coefficient of the at least one crystallization preventing layer in the visible light band is less than or equal to 1×10−5.
 14. The phase shifting device of claim 9, wherein the at least one dielectric layer comprises a crystalline material having a grain size that is less than or equal to 100 nm or an amorphous material.
 15. The phase shifting device of claim 9, wherein the thickness of the at least one dielectric layer is within a range of 50 nm to 500 nm, and the thickness of the at least one crystallization preventing layer is less than or equal 10 nm.
 16. The phase shifting device of claim 9, wherein a sum of thicknesses of all of the at least one crystallization preventing layer present in each phase shift pattern from among the plurality of phase shift patterns is less than or equal to 5% of a total thickness of all of the at least one dielectric layer and all of the at least one crystallization preventing layer present in each shift pattern from among the plurality of phase shift patterns.
 17. The phase shifting device of claim 9, wherein each of the plurality of phase shift patterns comprises a bar or a slit extending in a first direction, and the plurality of phase shift patterns are arranged in a second direction perpendicular to the first direction.
 18. A thin-film material comprising: alternately stacked dielectric amorphous layers and crystallization preventing amorphous layers, wherein a thickness of each of the dielectric amorphous layers is less than a thickness at which the dielectric amorphous layers crystallize, wherein an uppermost layer of the thin-film material is a dielectric amorphous layer, and wherein a root mean square value of a surface roughness of the uppermost layer is less than or equal to 2.5 nm.
 19. The thin-film material of claim 18, wherein a thickness of each of the crystallization preventing amorphous layers is less than the thickness of each of the dielectric amorphous layers.
 20. The thin-film material of claim 19, wherein the thickness of each of the crystallization preventing amorphous layers is less than or equal to 10 nm, and wherein the thickness of each of the dielectric amorphous layers is within a range of 50 nm to 500 nm.
 21. The thin-film material of claim 18, wherein a refractive index in a visible light band of the dielectric amorphous layers is greater than or equal to 2.4 and an extinction coefficient in the visible light band of the dielectric amorphous layers is less than or equal to 1×10−5.
 22. The thin-film material of claim 21, wherein an extinction coefficient in the visible light band of the crystallization preventing amorphous layers is less than or equal to 1×10−5.
 23. The thin-film material of claim 18, further comprising a plurality of structures formed on a substrate, each of the plurality of structures including the alternately stacked dielectric amorphous layers and the crystallization preventing amorphous layers.
 24. The thin-film material of claim 23, wherein a width of each of the plurality of structures is less than a wavelength of visible light, and wherein an interval between each of the plurality of structures is less than the wavelength of visible light. 